1. Field of the Invention
This invention pertains to viewing screens. More particularly, this invention pertains to viewing screens which increase brightness or gain in a predefined viewing area.
2. Description of the Prior Art
Viewing screens are used both in reflection and in transmission. In reflection, a viewing screen is typically made of a reflective flexible material that may be rolled up and stored when not in use. This type of screen is typically found in auditoriums, conference rooms, and residences where the screen is not in use frequently and is stored much of the time. In movie theatres, on the other hand, the reflective screen is usually secured to the front wall of the theatre.
In transmission, a typical viewing screen is of the "light box" type upon which the images, such as those from a slide projector, are incident, and the images are viewed from the opposite side of the screen. Transmissive viewing screens are typically made of a lenticular (or acetate) sheet which has numerous small lens-type structures machined in the screen. Another type of transmissive viewing screen is that found on large screen TVs which often have machined or formed therein a vertically oriented corrugated structure to permit wide angle viewing.
Each of these prior art viewing screens has significant shortcomings. First, particularly with respect to transmissive screens, their surface structure size is macroscopic leading to poor resolution if the size of the smallest elements of the image to be transmitted are smaller than the size of the surface structure of the screen. Furthermore, stronger and more expensive light sources must be used to generate sufficient brightness on the viewing side of the transmissive screen to offset low screen efficiency.
Second, prior art viewing screens generally do not have controllable fields of view and waste light energy by directing light into areas from which the screen is not viewed. Those that are controllable, such as lenticular screens, have large grain structure making them unsuitable for certain applications, such as HDTV (high definition television).